Annex 1 —Transport System Details Subsea Power Cable Subsystem
5.5 Conclusions and Recommendations
The combination of different activities offshore influences the assessment of risks arising from multi-use offshore platforms. The exact details of the processes involved in such multi-use offshore activities are still unknown and hence esti-mations are uncertain.
The main risk of a combined wind-mussel farm investigated here is that of a drifting aquaculture construction. Two major scenarios and related questions were investigated:
1. Is there a risk that a drifting aquaculture constructions strikes the turbine foundation and causes a significant damage to the foundation?
2. What is the risk if a drifting aquaculture construction gets stuck around the turbine foundation and thus increases its surface area? Can the foundation handle the extra (drag) forces involved?
A preliminary qualitative assessment of these scenarios yields that scenario 1 (impact between offshore aquaculture and wind turbine foundation) is not a real threat in case of mussel and seaweed farms. It is highly unlikely that aquafarm structures will be used that are heavy and rigid enough to cause significant struc-tural damage. The (anticorrosive) paint of the turbine foundation might get dam-aged in case of an impact, but this will not lead to short term structural damage. In order to prevent corrosion and damage risks in the long term, appropriate actions (i.e. repair) can and should be taken. Forfish farms the situation in scenario 1 may vary with the type and size of cages that are used and the way they are constructed.
Potential risks of consequences of the impact should be assessed already in the design phase of such combined infrastructure.
Scenario 2 (extra drag force from currents and waves due to stuck aquaculture constructions) poses a risk especially to jacket constructions because it may lead to (strong) increase of frontal surface area of the immersed structure and thereby give increased drag forces. With monopiles and gravity based constructions the stuck aquaculture material may attach to the turbine foundation at a single point only with insignificant increase of frontal surface area and minimal increase in such drag force.
Table 5.3 Scenario 2: Drifting of the aquaculture
Mussels Seaweed Fish
Monopile No significant increase in loads expected Jacket Increase in drag force
Gravity based No significant increase in loads expected
The aquaculture is stuck around the turbine foundation. Grey cells indicate the worst case scenario
For a jacket construction, in the extreme case of a 100% coverage of its underwater surface by stuck aquaculture material during a storm, the overturning moment at the seabed could increase by 200–300 MNm (Janssen and van der Putten2013), and eventually lead to the collapse of the wind turbine. However, this risk is merely theoretical, considering the type and construction of aquaculture materials being far less massive than the foundation itself and the unrealistic assumption of a 100% coverage. Nevertheless, appropriate methods to avoid this small risk can be investigated in the design phase of such infrastructure, for instance modular aquaculture structures that fall apart in case of drifting under severe conditions.
In severe storms with extremely high waves, an intact aquaculture structure that is physically directly connected to the turbine foundation could theoretically lead to the collapse of the turbine if the overturning moment at the seabed becomes too large. For this reason, the investigated scenarios only consider aquaculture instal-lations that are not attached to any wind turbine foundations (Lagerveld et al.2014).
Nonetheless, if a connected wind farm-aquaculture infrastructure is considered and designed, methods to reduce and prevent high tensile forces on the turbine foun-dation should be taken into account. For example, use of suitable anchors to hold the aquaculture structure in place or application of so-called safety wires that break at predefined tensile forces. Although the aquaculture farm will be lost in the latter case, the turbine foundation will stay intact.
Finally, a few recommendations for the future implementation of a multi-use platform offshore, based on Noël (2015); van der Putten (2015) and Lagerveld et al.
(2014):
• Appropriate measures should be taken to protect aquaculture and offshore wind constructions from corrosion attack either by selection of corrosion resistant materials or by application of suitable protective techniques or coatings.
• Type and size of aquaculture activities determine the extent of effects on water and sediment quality. In turn, water and sediment quality may affect corrosion resistance of the materials used. This aspect should be dealt with in a dedicated risk assessment for the specific location.
• Maintenance aspects of materials for both offshore wind and aquaculture con-structions should be taken into account already in the design phase to ensure optimal lifetime of infrastructure.
References
Bartoli, M., Nizzoli, D., Naldi, M., Vezzulli, L., Porrello, S., Lenzi, M., et al. (2005). Inorganic nitrogen control in wastewater treatment ponds from a fish farm (Orbetello, Italy):
Denitrification versus ulva uptake. Marine Pollution Bulletin, 50, 1386–1397.
Beech, I. B., & Campbell, S. A. (2008). Accelerated low water corrosion of carbon steel in the presence of a biofilm harbouring sulphate-reducing and sulphur-oxidising bacteria recovered from a marine sediment. Electrochimica Acta, 54, 14–21.
Buck, B. H., Ebeling, M. W., & Michler-Cieluch, T. (2010). Mussel cultivation as a co-use in offshore wind farms: Potential and economic feasibility. Aquaculture Economics &
Management, 14(4): 255–281.
Burak Cakaloz, A. (2011). Fish cage construction. Presentation at the FAO Regional Training on the Principles of Cage Culture in Reservoirs. Issyk-Kul, Kyrgyzstan, 22–24 June 2011.
Retrieved July 27, 2016 from http://www.fao.org/fileadmin/templates/SEC/docs/Fishery/
Fisheries_Events_2012/Principles_of_cage_culture_in_reservoirs/Fish_Cage_Construction.pdf.
Buzovkina, T. B., Aleksandrov, V. A., & Shlyaga, L. I. (1992). Influence of the initial fouling on the marine corrosion of steel. 3, 501–503.
Callow, J. A., & Callow, M. E. (2011). Trends in the development of environmentally friendly fouling resistant marine coatings. Nature Communications, doi:10.1038/ncomms1251.www.
nature.com/naturecommunications.
Dean, R. J., Shimmield, T. M., & Black, K. D. (2007). Copper, zinc and cadmium in marine cage fish farm sediments: An extensive survey. Environmental Pollution, 145, 84–95.
Janssen, M. M. H. H., & van der Putten, S. (2013). Mechanical risks involved with aqua farming on offshore wind farm sites. TNO-MEM-2013–0100000996.
Kalantzi, I., Shimmield, T. M., Pergantis, S. A., Papageorgiou, N., Black, K. D., & Karakassis, I.
(2013). Heavy metals, trace elements and sediment geochemistry at four mediterraneanfish farms. Science of the Total Environment, 444, 128–137.
Kawahara, N., Shigematsu, K., Miura, S., Miyadai, T., & Kondo, R. (2008). Distribution of sulfate-reducing bacteria in fish farm sediments on the coast of southern fukui prefecture, Japan. Plankton and Benthos Research, 3, 42–45.
Lagerveld, S., Röckmann, C., & Scholl, M. (2014). A study on the combination of offshore wind energy with offshore aquaculture. IMARES Report C056/14. Retrieved October 12, 2015, fromhttp://edepot.wur.nl/318329
Loucks, R. H., Smith, R. E., Fisher, C. V., & Fisher, E. B. (2012). Copper in the sediment and sea surface microlayer near a fallowed, open-netfish farm. Marine Pollution Bulletin, 64, 1970–
1973.
Mantzavrakos, E., Kornaros, M., Lyberatos, G., & Kaspiris, P. (2007). Impacts of a marinefish farm in Argolikos Gulf (Greece) on the water column and the sediment. Desalination, 210, 110–124.
Msuya, F. E., & Neori, A. (2008). Effect of water aeration and nutrient load level on biomass yield, N-uptake and protein content of the seaweed Ulva lactuca cultured in seawater tanks. Journal of Applied Phycology, 20, 1021–1031.
Noël, N. (2015). Microbial influenced corrosion (MIC): Assessing and reducing the risk. Invited presentation at 2nd Annual Integrity and Corrosion of Offshore Wind Structures Forum, June 1–3, London, UK.
Nordvarg, L., & Johansson, T. (2002). The effects offish farm effluents on the water quality in the Aaland Archipelago, Baltic Sea. Aquacultural Engineering, 25, 253–279.
Robertson-Andersson, D. V., Potgieter, M., Hansen, J., Bolton, J. J., Troell, M., Anderson, R. J., et al. (2008). Integrated seaweed cultivation on an abalone farm in South Africa. Journal of Applied Phycology, 20, 579–595.
Valdemarsen, T., Bannister, R. J., Hansen, P. K., Holmer, M., & Ervik, A. (2012). Biogeochemical malfunctioning in sediments beneath a deep-waterfish farm. Environmental Pollution, 170, 15–25.
Van der Putten, S. (2015). Joint Industry project Felosefi. Improved fatigue crack growth models taking into account load sequence effects. Presentation at 2nd Annual Integrity and Corrosion of Offshore Wind Structures Forum, June 1–3, London, UK.
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Aquaculture Governance
Aquaculture Site-Selection and Marine Spatial Planning: The Roles of GIS-Based Tools and Models
Vanessa Stelzenmüller, A. Gimpel, M. Gopnik and K. Gee
Abstract Around the globe, increasing human activities in coastal and offshore waters have created complex conflicts between different sectors competing for space and between the use and conservation of ocean resources. Like other users, aquaculture proponents evaluate potential offshore sites based primarily on their biological suitability, technical feasibility, and cost considerations. Recently, Marine Spatial Planning (MSP) has been promoted as an approach for achieving more ecosystem-based marine management, with a focus on balancing multiple management objectives in a holistic way. Both industry-specific and multiple-use planners all rely heavily on spatially-referenced data, Geographic Information System (GIS)-based analytical tools, and Decision Support Systems (DSS) to explore a range of options and assess their costs and benefits. Although ecological factors can currently be assessed fairly comprehensively, better tools are needed to evaluate and incorporate the economic and social considerations that will also be critical to identifying potential sites and achieving successful marine plans. This section highlights the advances in GIS-based DSS in relation to their capability for aquaculture site selection and their integration into multiple-use MSP. A special case of multiple-use planning—the potential co-location of offshore wind energy and aquaculture—is also discussed, including an example in the German EEZ of the North Sea.
V. Stelzenmüller (&) A. Gimpel
Thünen-Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany e-mail: [email protected]
M. Gopnik
Independent Consultant, Washington DC, USA K. Gee
Helmholtz Zentrum Geesthacht, Max-Planck-Str. 1, 21502 Geesthacht, Germany
© The Author(s) 2017
B.H. Buck and R. Langan (eds.), Aquaculture Perspective of Multi-Use Sites in the Open Ocean, DOI 10.1007/978-3-319-51159-7_6
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